The invention relates generally to cast concrete culverts and particularly to a method and apparatus for fabricating three-sided, rectangular and skewed culverts.
The use of concrete as a construction material is synonymous with the fabrication of sewer pipe, culverts and smaller bridges. Concrete's load bearing ability, resistance to environmental and service related deterioration and cost, support its claim as the basic and preeminent heavy construction material.
While being formed into a useful product, it must, however, be contained within a suitable form, as is well known. The expense of such a form or forms often represents a significant if not major portion of the total cost of a concrete structure, particularly if the forms are specially constructed to produce it. On the one hand, a durable, reusable, often metal form may be relied upon to fabricate thousands of standard pieces such as pipes or septic tanks. On the other hand, unique structures may require one of a kind wood forms constructed by skilled carpenters at significant expense. Such forms are filled, stripped from the product and oftentimes destroyed, due to the significant labor expense attendant recovery of the individual form components.
It is therefore not surprising that significant effort has been directed toward producing forms that are adjustable, readily strippable and reusable.
One such form is disclosed in U.S. Pat. No. 2,265,871 to Scott. In the apparatus disclosed, a plurality of relatively small panels are releasably secured to one another to construct a form of the desired shape. Although the form components are reusable, it appears that significant assembly and breakdown time by relatively skilled labor would be required in order to adjust the form and thus the size and proportions of culverts fabricated with it.
Another concrete form on a somewhat larger scale is disclosed in U.S. Pat. No. 3,693,927 to Jennings. Here, the forms are used in the construction of box culverts or modular buildings. A pair of inner frame units are connected together for relative bidirectional motion and support a top (ceiling) panel forming member and release plate. While providing a readily reusable form, this apparatus is adjustable only over a certain limited range. Furthermore, over this limited range or any other initially chosen limited range, the cost of initially fabricating the casting apparatus appears to be significant and in view of its limited adjustability might render production costs of a small number of units unacceptably high.
U.S. Pat. No. 3,696,177 discloses another means for forming concrete box culverts and similar structures. This patent discloses a structure and apparatus similar to that discussed immediately above. That is, mold sections which are bidirectionally translatable define and support the inner and outer surfaces of the culvert. The form sections are fabricated of steel. When the concrete is set, the forms are moved away from the completed structure and may then be readily reused. Here, too the range of adjustability of a given form is limited and the initial expense of fabricating the form appears to be significant.
One difficulty with all of the foregoing devices is that they are intended to fabricate only four sided, rectilinear (right angle) culvert structures and the like, that is, structures wherein the planes of the sidewalls are perpendicular to the transverse axis of the top panel and wherein the opening is uniform in cross section and perpendicular to the transverse axis of the top panel. It has been found, however, that in the natural world not all streams, rivers, railroads and highways intersect at right angles. While all rectilinear culverts may be utilized to span an angularly oriented obstacle, they do not accomplish this task efficiently in that they must be of a span sufficient to accept the total angular width of the obstacle. Thus, the above discussed devices do not allow for the fabrication of culverts which most efficiently provide a crossing over obstacles oriented at angles other than right to the path of crossing. By way of contrast, a culvert wherein the opening is oriented obliquely relative to the top panel at approximately the same angle as the angle between the obstacle and the crossing path minimizes the span width as well as the total amount of material in the culvert.
A second difficulty of the discussed adjustable forms is their dedication to construction of standard box culverts. Significant benefits such as material saving and attendant reductions in transportation and construction costs flow from the construction of three sided (bottomless) culverts according to our co-owned invention set forth in U.S. Pat. No. 4,564,313 which is hereby incorporated in its totality by reference. Adjustable forms for the production of skewed, three sided culverts have not heretofore been available.
From a review of the prior art it is thus apparent that improvements in the art of culvert structures as well as their forms and construction methods are both desirable and possible.